1. Field of the Invention
This invention relates to negatively charged liquid developers for use in electrostatic photography, which contain novel highly negatively charged toners. The developers are particularly characterized by their stable polarity and the dispersibility of the toners. The developers may be in either concentrated or dilute form as described herein.
2. Description of the Prior Art
Negatively charged liquid developers for use in electrostatic photography have been broadly used for negative-positive development of electrophotographic photosensitive papers and electrostatic recording papers. Toners used for such liquid developers are usually prepared by blending and kneading colored particles, i.e. pigment or dye particles with a resin, a fat or an oil acting as a polarity-controlling and dispersion-stabilizing agent. Typical of such resins, fats and oils which have been employed are natural products such as rosin, dammer and linseed oil, phenol and alkyd resins modified with such natural products, and synthetic products such as silicone and acrylic resins. In the conventional negatively charged liquid developers, since the charge capacity of the toner particles is very low, the polarity is unstable and readily reversed. The results are that the dispersibility of the toner is poor, and images having high concentration cannot be obtained. Further, since the particle size of the toner is small, ground contamination is extreme with the result that images poor in sharpness are obtained. Moreover, in cases where natural products or resins modified with the natural products are employed, the properties and composition of the toner are varied, and it is difficult to obtain liquid developers of uniform quality.